It is known to use the exhaust gases issuing from the cylinders of an internal-combustion engine to drive a turbine which in turn drives a compressor that acts as a turbocharger for the cylinder intakes. In this manner the energy in the exhaust gases is exploited to increase the engine efficiency by compressing the air fed into the engine and mixed with the fuel.
The main problem in such a system is that the fresh-air requirements for the engine, the exhaust-manifold pressure, and the efficiency of the turbine and compressor all vary independently of each other. Thus if a compressor is provided which is driven at full speed when the engine is operating relatively slowly, too much air will be provided at higher speeds so that the ignition peak pressure will be exceeded and knocking will result. Similarly if a smaller compressor is provided the exhaust-manifold pressure at low speeds will be insufficient to operate it fast enough to supply sufficient air for operation.
Various arrangements have been suggested to overcome this matching problem, normally employing relative complex clutches and valve arrangements none of which have been found to be satisfactory or sufficiently simple for use in a motor vehicle where engine speed varies enormously and the entire system must be as compact and rugged as possible.